This invention relates to an injection control system for use with a fuel injection valve for internal combustion engines, and more particularly to an electronic fuel injection control system which is capable of electronically controlling the injection pressure, valve opening pressure, injection timing, injection period, etc. of the injection nozzle of a fuel injection valve.
A conventional Diesel engine is provided with a fuel injection valve which is projected into each cylinder of the engine. The fuel injection valve is supplied in an injecting manner with fuel from a fuel injection pump by way of an injection pipe, to inject it into the cylinder. Unit injectors are also conventionally used which are each a one-piece combination of a fuel injection valve and a fuel injection pump formed of a solenoid valve or the like and in which the fuel injection valve is supplied directly with fuel from the fuel injection pump to carry out injection of the fuel.
The fuel injection quantity Q obtained by those conventional fuel injection valves is determined by an equation of Q=CAt.sqroot.P, provided that A represents the effective opening area of the injection nozzle, t the injection period, and P the injection pressure (kg/cm.sup.2), respectively. Therefore, the fuel injection quantity Q can be controlled by varying the variables A, t, P.
Fuel injection systems conventionally used in Diesel engines employ a system in which the fuel injection quantity is controlled by changing the injection period. However, to change the injection period for control of the fuel injection quantity can unfavorably affect the engine combustion, which conventionally caused problems of exhaust gas and combustion noise as well as horsepower. According to those conventional fuel injection systems are capable of changing the fuel injection pressure. However, the change of the fuel injection pressure merely depends upon the engine rpm. No fuel injection system which is capable of positively controlling the fuel injection pressure has been proposed as yet. There have been proposed fuel injection systems of the type changing the valve opening pressure of the injection nozzle so as to control the lift of the nozzle needle. However, these systems are only capable of controlling the injection beginning and the injection end, but are not capable of controlling the injection rate.